Spectacles

Spectacles

Apart from the power of the lenses, there are many options to consider when choosing spectacles. The information in this section will help you understand the options. Your optometrist can provide the best advice on what will suit you.

A ‘triangular’ face (broader at the jaw than at the eyeline) needs a strong, dominant frame the same width as the jaw to provide balance.

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Why are some frames more expensive than others?

The cost of frames is partially based on fashion, with ‘designer-labels’ often costing more. Generally price is also related to the quality of the frame.

Metal frames, which require more skilled operations in their production, are generally more expensive. For example, titanium frames are almost indestructible, but cost considerably more than regular metal frames, while frames with high quality gold finishes will also cost more.

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Lenses

Single vision

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are the most commonly prescribed lenses;

have only one power in the lens;

allow you to see clearly in either the distance or at near; and

are worn most by younger people.

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As people get older, they gradually lose the ability to alter the focus of their eyes (‘presbyopia’).

Between the ages of 40 and 50, wearers develop a need for corrective lenses for both distance and near vision. They can use two pairs of single vision spectacles or one pair of multifocal lenses.

Multifocal lenses

There are three main types of multifocal lenses: bifocal, trifocal and progressive.

Bifocal lenses have:
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a top segment for distance

a lower segment for close tasks, i.e.: reading

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Trifocal lenses have:
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a top segment for distance;

a middle segment for intermediate distances; and

a lower segment for close tasks.

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There is a distinct dividing line between the segments of bifocals and trifocals.

allows the wearer to focus on all distances, there being a gentle change from distance to intermediate to near focus as one looks through different parts of the lens;

provide more natural vision than bifocals or trifocals;

are aesthetically more attractive; and

are popular with people who feel the dividing lines in bifocals and trifocals make them ‘look old’.

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Refractive index

The refractive index is a measure of the speed of light passing through a material. This influences how much a lens made of that material bends the light.

Glass and plastic lenses are available with different refractive indexes.

A higher refractive index allows lenses to be thinner. High refractive index materials are useful for people with high prescriptions, as they avoid the ‘coke bottle’ appearance of thick lenses. High refractive index lenses are more expensive than standard plastic and glass lenses.

Lens materials

There are three types of spectacle lens materials: glass, resin (plastic) and polycarbonate.

Glass:
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has excellent optical properties;

is reasonably scratch-resistant; and

is inexpensive.

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However, glass is heavier than plastic and polycarbonate, and breaks easily. Glass is unsuitable for sportspeople or those exposed to potential impacts.

Hard resin is:
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the most common lens materials;

usually called ‘plastic’ or sometimes ‘CR39’- the trade name of the first resin widely used for making lenses;

lighter than glass lenses;

more impact resistant but are usually slightly thicker; and

more prone to scratching unless they have a scratch-resistant coating.

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There is little difference in the cost of plastic and glass lenses with the same prescription.

Polycarbonate lenses are:
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highly impact resistant;

the material of choice for safety and sporting applications;

thin and light, although their optical quality may not be as good as glass or resin (particularly in high powered lenses).

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Tints and coatings

Tints:
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are generally used for sun protection;

can also be used for fashion purposes; and

can be almost any colour. Grey tints are generally the best for preventing glare, as they do not distort colour perception. Colour perception is important for recognising traffic signals.

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Coatings:
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reduce scratching; and

help extend the life of a pair of spectacles, although no coating can prevent all scratches.

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When purchasing plastic lenses make sure that they have a scratch resistant coating.

Anti-reflection (AR) coatings:
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reduce reflections from the lens surfaces; and

increase the amount of light that passes through the lens. The extra light improves vision, particularly for older people.

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Reduced reflection enhances the appearance of spectacles, and improves the appearance of higher powered lenses and high refractive index materials.

Photochromatic lenses

Photochromatic lenses automatically adjust for the amount of light present. A chemical incorporated in the lens becomes darker as it absorbs ultra-violet light. The more sunlight, the darker the lenses become.

Photochromatic lenses:
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allow spectacles to function as prescription sunglasses, as well as regular spectacles;

are available in a range of tints, in both glass and resin materials;

generally take a few cycles of darkening and fading to reach their full efficiency. They become darker and change more quickly after some use; and

are temperature sensitive (generally noticeable only if left on the dashboard of a car in summer, for example).

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Photochromatic resin lenses may fade after a few years.

Lens costs

Depending on the exact type, spectacle lenses can vary between $50 and $500 per pair.

The cost depends on factors such as:
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lens design;

lens material;

coatings;

tints; and

the prescription.

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Generally more complex lens designs are more expensive, so that progressive lenses cost more than bifocals, which in turn cost more than single vision lenses.

High refractive index materials are more expensive than lower refractive index materials, so that for a given prescription, thinner lenses will cost more than thicker lenses.

Tints or anti-reflective coatings will add to lens cost.

Lenses to correct high or complex prescriptions have to be custom ground and so cost more.

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Caring for your spectacles

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Clean your spectacles regularly.

Rinse them thoroughly to remove any dust or grit that could scratch the lenses, then wash them with soap and luke-warm water, and rinse.

Don’t use hot water as it can damage lens coatings and plastic frames.

Use a soft toothbrush to clean nose pads and hinges.

Remove stubborn marks on lenses using methylated spirits.

Never use other solvents as they can damage your frames.

Be careful when using hair spays or other sprays – they can coat the lenses and reduce your vision.

When you put spectacles down make sure the lenses do not touch anything. This will help keep them scratch-free and bright.

Keep spectacles in a protective case.

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Putting on and removing your spectacles

To put your spectacles on:
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hold the side pieces halfway down and push them gently over your ears.

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To remove your spectacles:
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hold them mid-way down the side pieces;

raise them so that they clear your ears; and

slide the spectacles forward. This way you will not disturb their alignment.

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Always use two hands to put your spectacles on and take them off. Using one hand will flex the frame and over time will reduce the proper fit.

Your glasses will need adjustment. Typically your glasses will slip down your nose or become uncomfortable. Visit your optometrist to have them re-adjusted.